Effects of thidiazuron and benzyladenine on axillary shoot proliferation of three green ash (Fraxinus pennsylvanica Marsh.) clones

Abstract

Mature seeds of three green ash (Fraxinus pennsylvanica Marsh.) clones, SD1009 (South Dakota origin), SD2002 (South Dakota origin), and KA2018 (Kansas origin) were cut to remove the apical portion and germinated on Murashige and Skoog (1962) salts with B5 vitamins (Gamborg et al., 1968) (MSB5) medium without plant growth regulators. Stable axillary shoot establishment was achieved for all three clones by subculture on MSB5 medium containing a combination of 5 μM thidiazuron (TDZ), 5 μM 6-benzyladenine (BA), and 1 μM indole-3-butyric acid (IBA). Following shoot establishment, axillary shoots were placed on MSB5 medium containing a single treatment of TDZ (1, 5, 10, 20, or 40 μM) or BA (1, 5, 10, 20, 40, or 80 μM). Concentration of TDZ and BA significantly affected shoot biomass (total dry weight of axillary shoots), with 10 μm TDZ or 40 μm BA providing maximum shoot proliferation with all three clones. Significant clonal differences also were noted in the proliferation of axillary shoots, with clone SD1009 exhibiting the highest axillary shoot proliferation. Axillary shoots were rooted under ex vitro conditions and acclimatized to the greenhouse.